Seat belts are a recognised primary occupant protection feature for automobiles. They have such a significant beneficial impact in reducing the incidence of injuries and death in collisions that their installation has long been mandated as an essential item of safety equipment.
It is equally known that the incidence of use of seat belts falls well below the desirable level of complete use by all vehicle occupants. Initially, coercive schemes for forcing seat belt use were imposed. The most famous such was a short lived federal regulation that mandated interlocking the vehicle engine with a seat belt sensor so that the vehicle could not be started unless all seat belts were fastened. An intense consumer reaction to this regulation led to its cancellation. Coercive schemes still remain, notably in the existence of State Seat Belt usage laws.
Currently, effort in the area of vehicle occupancy restraints centers on passive devices which do not require occupant cooperation for their function. Air bags are the currently ultimate passive restraint. However, Air bags are principally useful for protection against forward collision forces; they provide little protection against side impacts. Further, a significant proportion of crash injuries and deaths occur as a result of second impacts: the vehicle, as a result of the first impact, is projected into a second, usually more severe second impact. Air bags provide protection for only a short time period, often deflating before the second impact, which leaves the occupant unprotected.
Passive seat belt systems, alone or in conjunction with Air bags, are the current mandated occupant restraint solution. These generally take the form of door mounted belts which enclose an occupant as the door is closed. Unfortunately, current designs only automatically fasten the shoulder harness, and a lap belt must be manually fastened. Users often do not fasten the lap belt, and as a result may be severely injured by the shoulder harness alone. Also, automatic belts can still be disconnected completely, and often are.